The present invention relates, in general, to electronics, and more particularly, to methods of forming semiconductor devices and structures.
In the past, the semiconductor industry utilized various methods and structures to form electro-static discharge (ESD) protection devices. According to one international specification, the International Electrotechnical Commission (IEC) specification commonly referred to as IEC 61000-4-2 (level 2), it is desirable for an ESD device to respond to a high input voltage and current within approximately 1 nano-second (the IEC has an address at 3, rue de Varembé, 1211 Genève 20, Switzerland).
Some of the prior ESD devices used a zener diode in combination with a P-N junction diode. In most cases, the device structures had a high capacitance, generally greater than about one to six (1-6 pico-farads). The high capacitance limited the response time of the ESD device and also was a load to the device that was connected to the ESD device. Some prior ESD devices operated in a punch-through mode which required the devices to have a very thin and accurately controlled epitaxial layer, generally less than about 2 microns, and required a low doping in the epitaxial layer. These structures generally made it difficult to accurately control the clamping voltage of the ESD device and especially difficult to control low clamping voltages, such as voltages of less than about ten volts (10 V). One example of such an ESD device was disclosed in U.S. Pat. No. 5,880,511 which issued on Mar. 9, 1999 to Bin Yu et al. Another ESD device utilized a body region of a vertical MOS transistor to form a zener diode at an interface with an underlying epitaxial layer. The doping profiles and thicknesses used for the ESD device resulted in a high capacitance and a slow response time. Additionally, it was difficult to control the low doping levels in the thin layers which made it difficult to control the breakdown voltage of the ESD device. An example of such an ESD device was disclosed in United States patent publication number 2007/0073807 of inventor Madhur Bobde which was published on Mar. 29, 2007.
Accordingly, it is desirable to have an electrostatic discharge (ESD) device that has a low capacitance, that has a fast response time, that reacts to both a positive and a negative ESD events, that has a well controlled clamp voltage, that is easy to control in manufacturing, and that has a clamp voltage that can be controlled to over a range of voltages from a low voltage to a high voltage.